Is a Horn Relay Necessary?

[Superhart]

I have a 1930 Model A street rod converted to 12 volt. I want to add an Ahooogah horn with its own dash mounted horn button. Is it necessary to install a second horn relay to operate this horn or can it be wired directly? I plan to leave the modern horns connected to the steering wheel horn button operational. Anyone have any insight about this? I figure there must be a reason why manufacturers use horn relays.